Circuitron A 5203 DT-3 Single-Direction Grade Crossing Detection Unit

Specifically deigned for use at grade crossings, using Opto-Sensors to detect the train. Output controls flasher, gates, bells, etc.
 
Single-direction unit for crossing where bi-directional detection is unnecessary, such as a mainline with trains traveling in only on direction. Operates with any train length. Completely independent of track power. Use in any scale. Requires 10-18V AC or DC input.